Metal discharge tube and apparatus



P 1939- D. v. EDWARDS 7 2,173,473

METAL DISCHARGE TUBE AND APPARATUS Filed Dec. 19, 1935 3 Sheets-Sheet l Qty- 3 Z 3 4w 3a 3 16 INVENTOR fimzp K ATTORNEYS.

Sept. 19, 1939. D. v. EDWARDS METAL DISCHARGE TUBE AND APPARATUS Filed Dec. 19, 1935 3 Sheets-Sheet 2 sumo/1 PUMP l ENTOR BY W M 201914 ATTORNEY INVENTOR am 5" M ATTORNEYS,

3 Sheets-Sheet 3 D V EDWARDS METAL DISCHARGE TUBE AND APPARATUS Filed Dec. 19, 1935 Sept. 19, 1939.

Patented Sept. 19, 1939 METAL DISCHARGE TUBE AND APPARATUS Donald v. Edwards, Montclair, N. J., assignor to Electrons, Inc. of Delaware, a corporation of Delaware Application December 19, 1935, Serial No. 55,230

7 Claims.

This invention relates to electron discharge devices having metal vessel walls sealed with vitreous seals, and has for its principal object to provide a device of this type which is simple in construction and adapted to be conveniently and efliciently degassed, either permanently if the tube is to be a hard vacuum tube, or preliminary to filling with a gaseous medium ormetallic vapor if the tube is to be of the gaseous type.

Heretofore in the evacuation of devices of this character it has been customary to heat the vessel while pumping the gas therefrom, but although the release of the absorbed gas from the electrodes and other parts of the tube is greatly accelerated by heating, the higher the temperature the faster the rate of release, the temperature to which it has been possible, in the past, to raise the parts has been limited by the softening of the vitreous seals which are used to seal conducting leads into the vessel. Consequently, in practice the heating temperature has been held below the softening point of the seal, with the result that an undesirably large amount of gas still remains.

In accordance with this invention it is permiss'ible to raise the temperature considerably above the melting point of the vitreous seal while sub- ,iecting the device to a vacuum, thereby attaining a discharge device from which much more of the gas is removed .than has heretofore been possible.

The invention will be better understood from the following detailed description of specific embodiments, together with the accompanying drawings, of which Fig. 1 is a perspective view of a discharge device having a metal base dish sealed to a metal shell by a glass seal, according to this invention, a portion of the outer seal being broken away;

Fig. 2 is a cross-section of the device shown in Fig. 1, illustrating the interior parts of the tube and the manner of sealing the tube after evacuation;

Fig. 3 illustrates a furnace and means by which the device of Figs. 1 and 2 may be exhausted and sealed; and

Figs. 4 to 10 inclusive illustrate modified forms of sealing and arrangements of tube elements.

Referring to the drawings the outer shell of the tube comprises two complementary metallic parts I and 2, preferably steel, adapted tobejoined by suitable sealing material 3 which preferably insulates the parts I and 2 from each other. One of the parts, preferably the bottom part 2, carries the tube elements and is provided with a suitable receptacle, such as the trough 4, for the sealing material. In Fig. 2 only two elements, a

cathode II and a heat shield 8, are shown, the part I serving as the anode, and the device as a whole operating as a rectifier only. Obviously other elements, such as a control grid or grids may also be mounted on part 2, or the parts may be arranged on either part I or part 2 to suit individual conditions. In the drawings the heat shield 8 of the can type is supported on the bottom 2 by uprights 9, cross braced by brace III, preferably welded to the support and shield. The cathode element II of suitable material, such as nickel, comprises one or more spirals of wire. one end of each spiral being welded to the upper end of the heat shield and the lower ends being welded to a plate l2, electrically connected to a conductor l3, insulated from the heat shield by insulation lie, and from the bottom 2 by insulation l6, whereby a heating circuit exists from conductor l3, spirals ll, heat shield 8,'support 9 and bottom 2, to terminal I comprising an extension tube formed on bottom 2.

The cathode coils ll may carry a suitable electron emissive coating such as barium oxide, barium nickelate, or be of the emissive character described in U. S. Patent No. 1,985,855, granted December 25, 1934, or the heater may indirectly heat an emissive can as, for example, shown in Patents No. 1,989,133 granted January 9, 1935 and No. 2,012,339. of August 27, 1935.

The conductor l3 carries a bell-shaped portion ll adapted to be immersed in the insulating medium 3a carried in the receptacle la formed in the bottom 2.

It will be seen that by lowering the bottom 2, as shown in Fig. 3, the depending rim i-a of part I, 'will be raised above the insulation, thus opening the interior of the tube to the atmosphere.

The apparatus for degassing the tube comprises a suitable chamber adapted to be heated by suitable means and evacuated by a pump, the chamber being provided with suitable means for supporting the tube in opened condition, e. g. bottom lowered as shown in Fig. 3. Such a chamber is provided by the bell 18 of quartz or other material impervious to air or gas and adapted to withstand a high temperature. The bell is mounted on a base plate It, preferably of metal, to which it may be sealed by a waxed or greased ground joint at 20. A metal cylinder 2| having a horizontal strengthening web 22 is provided for supporting the shell, as shown. The lower end of cylinder 2i rests on the head 23 of a supporting cylinder 24, preferably of quartz, which is mounted on the base plate IS. A metal cylindrical sleeve 25, closed at the lower end in a manner to retain a vacuum within the sleeve, and having a metal plug or crosshead 26 adapted to slide Within it, is positioned within cylinder 24 and through the base plate I9, to which it is welded. The sleeve 25 is provided with an exhausting pipe 21.adapted to be connected with a vacuum pump 28-through a valve 29. The closed sleeve and the bell are adapted to be evacuated by the pump; and to equalize the pressure in the bell and sleeve there are provided vents 30, 3I and 32, respectively, through members 26, 23 and -22.

The tube with its bottom 2 lowered is placed on the supporting cylinder 2| and with the tube I4 protruding downwardly through centrally located openings in the web 22 and crosshead 26. The end of the tube I4 is fitted into a collar 33 threaded into the crosshead 26, and the conductor I3 is threaded into a block 34 insulated from the crosshead 26 by insulating material 35. The tube I4 is then held in place by a set screw 36, a suitable opening 36a being provided to give access through support 24 and sleeve 25 thereto.

A conductor 31 welded to block 34 passes down through a suitable insulator 38 and through a close fitting rubber hose 39, in which 38 is mounted, to the outer atmosphere, and a similar rod 40 extends down from the crosshead 26 through a similarly mounted insulator 4| and rubber hose 42. The hoses 33 and 42 are of the type known as vacuum hose; they fit tightly over the respective depending mouths 43 and 44 of the sleeve 25 integral with the base of the sleeve 25, and fit snugly around the rods 3'! and 4|] in a manner to permit vertical movement of the rods through the hoses without permitting the entry of gas into the sleeve 25. The outer ends of rods 31' and 40 are attached to a block 45 operable in a vertical direction by a lever 46 pivoted to a fulcrum 41 so that the rods 31 and 40 may be moved upwardly or downwardly through the vacuum hose to move the crosshead 26 in a vertical direction.

A furnace 48 is supported above the vacuum bell and adapted to be lowered over and around the part of the bell within which is located the shell and dish. Details of the furnace are not shown, but it may be of the gas or electric type, or may simply be a coil carrying a high frequency current which induces a large heating current in the shell I and bottom part 2, and also in the metal supporting cylinder 2I.

The sealing compound should be a substance which is stable and has a temperature coeflicient somewhere near or higher than that of the metal to be sealed, and should also create an elastic, tough glass or vitreous material having the property of not frothing under heat and vacuum, and not rupturing while or after cooling.

I have found a vitreous substance prepared in the following manner to be satisfactory. A mixture of silica, an oxide of iron and sodium silicate may be melted at atmospheric pressure in the following proportions:

Compound oportion by weight Percent S102 28 N12SiO3.5HgO 53 F6304 19 greater detail and claimed in my copending application, Serial No. 101,059 filed September 16, 1936 as a division of the present application.

To exhaust the tube it is supported as shown in Fig. 3 with the outer shell I resting upon the support 2I and with the extension I4 of the bottom part 2 lowered, whereby the rim of the shell I is above the level of the broken pieces of glass 3 and 3a in the troughs formed in the bottom portion 2, thus separating the opening between the two parts of the shell. The bell I8 is placed over the tube and sealed to the base I9. By means of the pump 28 the bell and the tube are preliminarily exhausted. The furnace 48 surrounding the bell I8 is then heated to a temperature higher than the melting point of the glass. The only real limitation on the temperature is the melting point of the metal, although it is advisable to keep the temperature below the point at which the metal evaporates rapidly. A recommended degree of degassing in the case of the steel vessel is that produced when the vacuum is pumped to about 5 10- millimeters of mercury while the vessel and its contents are heated to about 1000 C., which is the temperature at which steel begins to evaporate rapidly. If the parts are clean about a half hour is usually required to create this degree of vacuum.

During the heating and evacuating, the filament is preferably heated by applying a voltage across the terminals of the rods 31 and 40. The pumping is continued until the cathode coating material is converted and all surface and dissolved gas is removed. The term converting" means placing the cathode coating material in its ultimate condition. For example, when barium carbonate is used to coat the cathode it is "converted when it has been changed by the heat to barium oxide, and the carbon dioxide released thereby is drawn ofi. During this process the glass melts to a liquid filling within the troughs 3 and 3a of the dish and is thoroughly degassed by the high temperature at the high vacuum.

When the device is adequately degassed the temperature is lowered as much as possible while still maintaining the glass liquid. The pump is then shut off by operating of valve 29. If the device is to contain a special gas filling such as argon for example, the correct amount of the gas is admitted to the vacuum chamber through a pipe 49 controlled by a valve 50. The crosshead 26 is then raised by lever 46 a distance suflicient to raise the bottom 2 until the molten glass 3 surrounds and embeds the lower edge of the part I but not sufilcient to cause the shell to contact with the metal trough. The position of the dish and shield, as thus elevated, is shown in Fig. 3 by dotted lines. When the shell rim is dipped into the molten glass the glass wets the metal parts and seals off the inside of shell I from the rest of the vacuum chamber.

The heat is then turned off entirely; and as the parts cool the glass sets, forming a strong vitreous seal.

When the evacuation is completed the set screw 36 is released and by turning the tube conductor I3 will be unscrewed from the contact block 34. The tube may then be withdrawn from its support. The tube is then suitably mounted to connect conductor I3 and sleeve I4 to the heating circuit. The cathode-anode circuit is established by connecting the part I with conductor I3 or with tube I4. Preferably part I serves as the anode; a suitable anode contact is shown at 5| in Fig. 2.

Ordinary steel is subject to corrosion at the temperatures frequently encountered in commercial rectiflers. To avoid corrosion the tube may be operated in an oil bath, which may also act as a cooling bath. Or, if the tube is air-cooled, the shell may be made of stainless steel, or coated with vitreous enamel or other corrosion resisting coating.

If desired the annular space between the two parts i and 2 above the insulation I may be filled in with an organic sealing compound such as tar 52 to protect the glass from atmospheric moisture, and also to prevent arcing when high voltages are applied to the electrodes. In Fig. 1 this sealing compound 52 is partly broken away to show the glass seal 3.

The temperature 01' heating, rather than the time of pumping, is the important factor in the degassing; for raising the temperature a few degrees liberates from the walls as much 01' the obnoxious substances in a few minutes as pumping a great many hours without the increase in temperature.

The high temperature reached according to this invention is facilitated by the unique form and location of the glass seals. The trough construction permits the glass to be melted and still remain in its proper place, so that upon cooling, the glass solidifies and forms a perfect seal.

Other modifications than that shown in Figs. 1 and 2 are possible. Examples of such are shown in Figs. 4 to 10. In all these figures except Figs. 6, 8 and 10 the discharge device is shown in vertical section, although the cathode and heat shield structure is not shown in section. In these figures, the filament is considered to be within the shield, and. is not shown; and one end of the filament is considered to be connected to the shield, as in Fig. 2.

In the modification of Fig. 4, a straight-sided shell I and a' base plate 2 are sealed by a glass seal 3 in an annular trough 4. The cathode shield 8 is supported by rods 9 and 9 welded to the trough 4. The connection to the free end of the filament is a rod i3 welded through bottom 2 and passing through an insulator H in heat shield 8 to the heater.

Fi 5 shows a modification in which the device is sealed at the top. Fig. 6 shows a top view oi. the device shown in vertical section in Fig. 5. The shell I is enclosed at the top and bottom except for two openings 53 and 53 at the top which have upwardly extending cylindrical walls. An upwardly extending elliptical cylinder 54 is welded to the top of the shell in the position shown. Rods 55 and 56, the latter of which is attached to the free end of the heater through an insulator 51, support the cathode and heat structure. These rods have welded thereto inverted metal cups 58 and 59.

This device may be sealed by placing above it a crucible containing molten glass and pouring the glass on to the top of the device within the elliptical cylinder 54 to seal the parts, as shown.

Figs. '7 and 8 show a construction which is nearly an inverted counterpart of that shown in Fig. 5, in which the cups 58 and 59 are placed at the bottom of the .shell instead of at the top. According to this method of making the device it is not necessary to pour the glass from a crucible; but instead, the glass may be melted in the cups. Since the cups hold the glass no other arrangement such as the cylinder of Fig. 6 is required.

Figs. 9 and 10 illustrate a modification in which the opening 80 in the shell is rectangular in shape and the trough ii is also rectangular. Fig. 10 is the bottom view. The cathode structure is supported by supports 52 and 63 of fiatcross-section, bent in the shape shown in Fig. 9 so that it does not touch either the shell or the trough. As many 01' these fiat supports or leads may be used as is desired; the number will depend on the number 01' electrodes. For a device having only cathode and anode electrodes, only two are required as in the case 01' previous modifications. There is shown a third lead 54 which may be used for a control grid. The trough BI is filled with the glass seal.

In the modifications shown in Figs. 5, 6, 7, 8 and 9 the filament and heat shield structures should first be placed within the shells, after which the cylindrical end sections 01' the shells should be welded in place.

Although there have been described electron discharge devices having only anode and cathode electrodes, it will be understood that other electrodes such as a control grid or grids may be added, if desired.

I claim:

1. A ventless vacuum tube comprising a steel vessel and a plurality of steel cover members placed to cover said vessel, said vessel and cover members being sealed, but electrically insulated from each other, by vitreous sealing substance to form a complete envelope, of which said vessel, cover members and sealing substance are the sole components, said seals being held within, and sealed to, steel troughs, each of said cover members being electrically connected to an electrode member within said tube.

2. A metal vacuum tube the envelope of which comprises a plurality of metal members, two of said members having an electrode structure, one of said two members having a trough and the other of said two members having a periphery which extends into said trough, but which does not contact with said trough, and a vitreous substance in said trough which seals said members together and insulates them from each other.

3. A metal vacuum tube comprising a metal vessel with a tubular rim at its open end, and a cover having metal members over said open end, said cover supporting an electrode within said tube, at least one of said members having a tubular rim, one of said members having trough means, said rims protruding into said trough means, and a vitreous sealing substance in said trough means which seals and insulates said rims from each other and from the trough means.

4. A metal vacuum tube comprising a steel vessel with a tubular rim at its open end and a cover having steel members over said open end, said cover supporting an electrode within said tube, at least one of said members having a tubular rim, one of said members having trough means, said rims protruding into said trough means, and a vitreous sealing substance in said trough means which seals and insulates said rims from each other and from the trough means.

5. A metal vacuum tube comprising three metal members forming the envelope of said tube, a first of said members being a vessel hav ing a rim at one end, a second of said members carrying an electrode terminal and having a rim, and the third of said members carrying another electrode terminal and having trough means, the rims of said first and second members extendingv into, but not touching said trough means, and a vitreous substance in said trough means which seals said rims to said trough means, but insulates said three members from each other to permit them to act as separate electrode terminals.

6. A vacuum tube comprising metal members and vitreous sealing material therebetween, said members and material forming the sole envelope of the tube, a trough-formed means, at ,least one of said members supporting, and being electrically connected to, an electrode structure within said tube, and at least one of said members containing a protruding neck which extends into said trough means, and a vitreous substance being adapted to seal the two members.

DONALD V. EDWARDS. 

